The present invention relates to optical recording regeneration apparatus and, in particular, to control means for modulation of a optical source at the time of information recording in such apparatus.
FIG. 2 shows the relationship between optical output in the form of power and drive current of a semiconductor laser illustrating that P-I properties are temperature dependent. At a general operating temperature T.sub.0 106 the oscillation threshold current I.sub.th is I.sub.th.sbsb.0. However, when the temperature of the semiconductor laser increases to T.sub.1, as indicated at 107, the P-I properties change requiring also a higher oscillation threshold current I.sub.th.sbsb.1. For a fixed drive current value I.sub.w at the time of recording, power of the write beam drops from P.sub.0 to P.sub.1 because of the temperature variation. When data recording is further attempted following such a temperature increase, recording is aggravated or the write pit length is shortened. Thus, in order to control and maintain a fixed optical output, present recording technology utilizes Automatic Power Control (APC) to monitor the optical output of the semiconductor laser using a photodiode feedback circuit.
Although it is possible to control the power of the write beam to a certain set value according to such prior art technology, it is not possible to detect whether the write power is most suitable at any point during recording, thereby making impossible control that responds to variations in the recording sensitivity of the disk resulting from temperature and other variations over time. FIG. 3 shows the relationship between regeneration pulse width and disk temperature when recording is accomplished while maintaining a fixed power for the write beam. When disk temperature rises from T.sub.1 to T.sub.2, recording sensitivity rises and the write pit lengths are increased so that regeneration pulse width widens from L.sub.1 to L.sub.2. However, the write beam power still slips away from the most desirable value and, as a result, the regeneration signal deteriorates in quality.